In recent years, the greenhouse effect due to CO2 has been pointed out as one of the causes of the global warming, and it has become an international urgent task to provide countermeasures to CO2 to protect the global environment against the warming. CO2 is generated by any human activities involving the combustion of fossil fuels, and there are increasing demands for suppressing CO2 emissions. Along with the increasing demands, studies are energetically being made on a CO2 reduction and recovery method, in which CO2 contained in flue gas emitted from industrial equipment, such as boilers or gas turbines, is reduced and recovered by bringing the flue gas in contact with an amine-based CO2 absorbent, and on an air pollution control system that stores the recovered CO2 without releasing it into the air, in order for the method and the system to work in power plants, such as thermal plants, that consume a large amount of fossil fuels.
A CO2 recovery apparatus has been proposed that performs, as processes for reducing and recovering CO2 from flue gas with the aid of the CO2 absorbent as above, a process performed in a CO2 absorber (hereinafter, also described as an “absorber”) in which the flue gas is brought into contact with the CO2 absorbent, and a process performed in an absorbent regenerator (hereinafter, also described as a “regenerator”) in which the CO2 absorbent that has absorbed CO2 is heated to isolate CO2 and the CO2 absorbent is regenerated and circulated back to the CO2 absorber for reuse (see, for example, Patent Document 1).
In the CO2 absorber, the flue gas is brought into counter-current contact with the amine-based CO2 absorbent, such as alkanolamine, (hereinafter, described as an “amine absorbent”), so that CO2 contained in the flue gas is absorbed by the CO2 absorbent due to a chemical reaction (an exothermic reaction) and the flue gas with CO2 reduced is released to the outside of a system. The CO2 absorbent that has absorbed CO2 is also referred to as rich solution. The pressure of the rich solution is increased by a pump. Thereafter, the rich solution is heated in a heat exchanger by a hot CO2 absorbent (lean solution), which has been regenerated by releasing CO2 in the regenerator, and then the rich solution is supplied to the regenerator.